This invention relates to a multicast/broadcast communication system for use in carrying out multicast/broadcast communication through both terrestrial and satellite communication networks.
Lately, delivery services or businesses through an internet has become popular more and more and consequently grown up rapidly. For example, music and movies tend to be delivered through the internet in response to users' requests and conferences and seminars also have been held among remote locations through the internet. Even internet school has been considered which educates pupils or students who live in remote places. In these applications, a huge amount of communication contents should be continuously transmitted without any interruption for a predetermined duration. Such continuous transmission will be collectively called bit streaming. Such bit streaming has been expected of rapid growth in the future but encounters difficulties in view of signal performance and a communication capacity when it is realized only by the internet.
The above-enumerated broadcast, remote conferences, remote lessons through the internet may establish promising businesses. In addition, such businesses will do well through a current internet as long as users are restricted to a small number. However, when participants or users are increased in number, it is difficult to provide sufficient services to the users only by the internet. For example, it is assumed that a certain internet broadcast station provides live broadcast or live program at a rate of 300 kbps and that ten thousands (10,000) of users access the internet broadcast station. This requires a communication path with a net capacity of 3 Gbps. In general, several times of the capacity (3 Gbps) are required to keep a sufficient quality of communication by using a packet exchange method. As a result, a communication path of 10 Gbps or more is needed. This makes it difficult to practically realize such internet broadcast in view of both signal processing and costs imposed on the path.
In order to solve the above-mentioned problem, consideration may be made about using a broadcast method such that the internet broadcast station carries out transmission at a rate of 300 kbps only to a nearest router. Herein, it is to noted in this method that a broadcast signal is delivered through the nearest router to all routers that are included in the internet.
In the meanwhile, the feature of the internet broadcast is that everybody can readily broadcast or transmit information through the internet. Taking this into account, it will be expected that internet broadcast stations explosively increase in number in the near future. For example, it is assumed that the internet broadcast stations increase in number to 1,000 in the internet. In this event, every one of the routers should cope with a communication traffic of 300 Mbps only for the internet broadcast. As mentioned before, a communication capacity of each router should have several times the communication traffic in order to maintain a sufficient quality of communication by using a packet exchange method. This shows that each communication path between adjacent routers should be 1 Gbps or more only for the internet broadcast. Accordingly, such a communication system can not be practically realized at the present.
Practically, a communication capacity or rate in the current internet is at most 50 kbps when a telephone line is used. Even when an ISDN is used, the communication capacity is as high as 64 kbps. In order to improve an access speed, various developments have been made about new technologies, such as ADSL (Asymmetric Digital Subscriber Line) and FTTH (Fiber To The Home). The former enables an access speed of about 1 Mbps while the latter enables an access speed of 100 Mbps.
Even when the access speed can be raised up, a recent problem is caused to occur in a speed of a broadband network. As well known in the art, the internet connects two points scattered in the world, through a lot of routers. With this structure, a long time is needed for communication or a packet is frequently discarded even when congestion takes place at a single router. This results in degradation of a quality of communication. In this situation, when senders or recipients in the internet broadcast are increased as mentioned before, overloads are imposed on the internet, which makes realization of such a network difficult.